Each optical communication apparatus includes an optical modulator which modulates light by making use of an electro-optic effect. Such an optical modulator is, for example, an optical waveguide device which modulates continuous wave (CW) light output from a laser by an electrical signal and which outputs the CW light (see, for example, Japanese Laid-open Patent Publication No. 2008-58436).
FIG. 22 is a plan view of an optical waveguide device. With an optical waveguide device depicted in FIG. 22, an optical waveguide 102 is formed over a dielectric substrate 101 which has an electro-optic effect, and an electrode 103 is formed over the optical waveguide 102. This optical waveguide device is a dual drive type optical modulator. Electric fields are formed on two waveguides 102a and 102b parallel to each other by two signal electrodes 103a and 103b respectively. By doing so, input light IN output from a laser is modulated and output light OUT is obtained.
With the optical waveguide device depicted in FIG. 22, positive data Data and negative data Data (indicated by Data with a bar in FIG. 22) which are complementary electrical signals are input to the two signal electrodes 103a and 103b, respectively, so that the optical waveguide device will perform push-pull operation. At this time it is necessary to modulate light propagating through the two waveguides 102a and 102b parallel to each other at the same timing. To be concrete, it is necessary that the data Data input to the signal electrodes 103a and 103b reach the parallel waveguides 102a and 102b at the same timing at a line 104 indicated in FIG. 22.
Therefore, the length of feed portions of the signal electrodes 103a and 103b from portions to which the data Data is input to the parallel waveguides 102a and 102b is adjusted. By doing so, the timing at which the data Data that are complementary electrical signals reaches the parallel waveguides 102a and 102b is adjusted. For example, as indicated in a frame 105 of the FIG. 22, the signal electrode 103b is bent to adjust the timing at which the data Data reaches the parallel waveguides 102a and 102b. 
Plural intrinsic modes of a microwave can propagate through the substrate 101. The distribution of an electric field and propagation speed for each intrinsic mode depend on the shape of a section of a chip. Coupling between a coplanar mode propagating through an electrode and an intrinsic mode (undesired mode) occurs at a frequency and loss occurs. This coupling tends to occur at a bend where the direction in which the coplanar mode propagates changes. As a result, loss tends to occur at a bend in the electrode. The more significantly an electric field of the coplanar mode overlaps with an electric field of the undesired mode, the stronger the coupling becomes. As an electric field of the coplanar mode spreads, usually the coupling becomes stronger. Therefore, as a gap between a signal electrode and an earth electrode becomes wider, loss becomes heavier. With an electronic device for which light is not used, a dielectric substrate through which light does not pass may be used.
However, a bent portion of an electrode differs from a straight portion in electric field distribution, so signal loss occurs.